The invention applies notably to systems using modulations that are rectilinear, or rendered quasi-rectilinear after preprocessing, such as certain friend-foe identification systems (IFF in modes S and 5) or even certain radio communication networks (cellular or otherwise) such as the Global System for Mobile communications GSM, for which the main source of interferences is the network itself.
The problem of synchronizing the links in the presence of interference is a problem that has been given enormous attention over the last two decades, mainly in the fight against co-channel interference in the context of multiple-access networks relying on a code or CDMA (code-division multiple access).
These techniques operate on the basis of one [1-2] or several [3-5] antennas [9] in reception. However, the single-sensor techniques are all very specific to the CDMA context and cannot be considered in F/TDMA networks (networks with multiple or time-division multiple access, with slow (or quick) time-frequency hopping (F-TDMA)). Also, the multiple-sensor techniques proposed in [4] [9] are similar whereas those derived from [3] also remain specific to CDMA networks in as much as the spreading codes are assumed to be not modulated randomly by information symbols. In fact, only the maximum likelihood approach proposed in [5] can be envisaged outside the CDMA context. However, this approach presupposes stationary Gaussian interferences, which are therefore second-order circular, and does not use any a priori particular ones of the interferences. In particular, the approach proposed in [5] becomes sub-optimal in the presence of second-order non-circular interferences, for which the second correlation function is not identically zero, a property characteristic of the GMSK signals used by the GSM networks in particular, which become quasi-rectilinear after preprocessing.